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Abstract:

According to various embodiments, a system includes a first cross-flow
filter configured to remove at least a first portion of a liquid from a
fuel slurry to increase a concentration of a solid fuel in the fuel
slurry. The system also includes a gasifier configured to generate a
syngas from the fuel slurry.

Claims:

1. A system, comprising: a first cross-flow filter configured to remove
at least a first portion of a liquid from a fuel slurry to increase a
concentration of a solid fuel in the fuel slurry; and a gasifier
configured to generate a syngas from the fuel slurry.

2. The system of claim 1, comprising a fuel slurry injector configured to
receive and inject the fuel slurry into the gasifier.

3. The system of claim 1, comprising a fuel slurry pump configured to
pump the fuel slurry along a slurry flow path having the first cross-flow
filter.

4. The system of claim 3, wherein the first cross-flow filter is disposed
in a slurry flow path downstream from the fuel slurry pump.

5. The system of claim 1, comprising an agitation system coupled to the
first cross-flow filter, wherein the agitation system comprises an
agitator configured to agitate the first cross-flow filter.

6. The system of claim 1, comprising a heating system coupled to the
first cross-flow filter, wherein the heating system comprises at least
one heater configured to heat the first cross-flow filter.

7. The system of claim 1, comprising a control system configured to
control removal of the liquid via the first cross-flow filter to adjust a
concentration of the solid fuel in the fuel slurry.

8. The system of claim 1, comprising a second cross-flow filter
configured to remove at least a second portion of the liquid from the
fuel slurry.

9. The system of claim 8, wherein the first and second cross-flow filters
are disposed in parallel along first and second slurry flow paths,
respectively.

10. The system of claim 8, wherein the first and second cross-flow
filters are disposed in series along a slurry flow path.

11. The system of claim 1, wherein the first cross-flow filter comprises
a plurality of slurry flow paths extending through an enclosure, wherein
each slurry flow path is surrounded by a filter medium.

12. The system of claim 1, wherein the first cross-flow filter comprises
a slurry flow path extending through an enclosure, wherein the slurry
flow path is surrounded by a filter medium, and the filter medium
converges in a downstream direction along the slurry flow path.

13. A system, comprising: a slurry concentration controller configured to
control a concentration of a solid fuel in a fuel slurry for
gasification, wherein the slurry concentration controller is configured
to adjust removal of a liquid from the fuel slurry via a cross-flow
filter.

14. The system of claim 13, comprising the cross-flow filter.

15. The system of claim 13, comprising a gasifier configured to generate
a syngas from the fuel slurry.

16. The system of claim 13, wherein the slurry concentration controller
is configured to control an agitation system to agitate the cross-flow
filter.

17. The system of claim 13, wherein the slurry concentration controller
is configured to control a heating system to heat the cross-flow filter.

18. A method, comprising: controlling a concentration of a solid fuel in
a fuel slurry at least partially by adjusting removal of a liquid from
the fuel slurry via a cross-flow filter; and gasifying the fuel slurry in
a gasifier downstream from the cross-flow filter.

Description:

BACKGROUND OF THE INVENTION

[0001] The subject matter disclosed herein relates to a system and method
for concentrating a solid fuel in a slurry prior to gasification.

[0002] Syngas may be produced by the gasification of a feedstock, such as
coal, and may be utilized as fuel, e.g., in an integrated gasification
combined cycle (IGCC) power plant. Prior to gasification, the feedstock
may be transferred to a gasifier by a pump. The feedstock may consists of
a slurry (i.e., a suspension of a solid fuel in a liquid). The ability to
pump the slurry, as determined by the slurry's viscosity and stability,
may determine and limit the concentration of the slurry. Prior to pumping
the slurry, the concentration of the solid fuel in the slurry may be
affected by the addition of surfactants. However, the concentrations
obtained with surfactants also may be limited to concentrations where the
slurry is stable and viscous enough for pumping. Thus, the inability to
obtain higher concentrations of the solid fuel in the slurry may limit
carbon conversion and cold gas efficiency during gasification.

BRIEF DESCRIPTION OF THE INVENTION

[0003] Certain embodiments commensurate in scope with the originally
claimed invention are summarized below. These embodiments are not
intended to limit the scope of the claimed invention, but rather these
embodiments are intended only to provide a brief summary of possible
forms of the invention. Indeed, the invention may encompass a variety of
forms that may be similar to or different from the embodiments set forth
below.

[0004] In accordance with a first embodiment, a system includes a first
cross-flow filter configured to remove at least a first portion of a
liquid from a fuel slurry to increase a concentration of a solid fuel in
the fuel slurry. The system also includes a gasifier configured to
generate a syngas from the fuel slurry.

[0005] In accordance with a second embodiment, a system includes a slurry
concentration controller configured to control a concentration of a solid
fuel in a fuel slurry for gasification, wherein the slurry concentration
controller is configured to adjust removal of a liquid from the fuel
slurry via a cross-flow filter.

[0006] In accordance with a third embodiment, a method includes
controlling a concentration of a solid fuel in a fuel slurry at least
partially by adjusting removal of a liquid from the fuel slurry via a
cross-flow filter. The method also includes gasifying the fuel slurry in
a gasifier downstream from the cross-flow filter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] These and other features, aspects, and advantages of the present
invention will become better understood when the following detailed
description is read with reference to the accompanying drawings in which
like characters represent like parts throughout the drawings, wherein:

[0008] FIG. 1 is a schematic block diagram of an embodiment of an
integrated combined cycle (IGCC) power plant utilizing a filter to
increase solid fuel concentration in a slurry;

[0009]FIG. 2 is a schematic block diagram of an embodiment of a
filtration system employed upstream of a gasifier;

[0010]FIG. 3 is a schematic block diagram of an embodiment of the
filtration system employing multiple filters in parallel;

[0011]FIG. 4 is a schematic block diagram of an embodiment of the
filtration system employing multiple filters in series;

[0012]FIG. 5 is a schematic block diagram of an embodiment of the
filtration system employing multiple flow passages within a filter;

[0013]FIG. 6 is a schematic block diagram of an embodiment of the
filtration system employing a converging filter; and

[0014]FIG. 7 is a schematic block diagram of an embodiment of the
filtration system employing agitation and heating systems.

DETAILED DESCRIPTION OF THE INVENTION

[0015] One or more specific embodiments of the present invention will be
described below. In an effort to provide a concise description of these
embodiments, all features of an actual implementation may not be
described in the specification. It should be appreciated that in the
development of any such actual implementation, as in any engineering or
design project, numerous implementation-specific decisions must be made
to achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which may vary from one
implementation to another. Moreover, it should be appreciated that such a
development effort might be complex and time consuming, but would
nevertheless be a routine undertaking of design, fabrication, and
manufacture for those of ordinary skill having the benefit of this
disclosure.

[0016] When introducing elements of various embodiments of the present
invention, the articles "a," "an," "the," and "said" are intended to mean
that there are one or more of the elements. The terms "comprising,"
"including," and "having" are intended to be inclusive and mean that
there may be additional elements other than the listed elements.

[0017] The present disclosure is directed to systems and methods for
concentrating a solid fuel (e.g., coal) in a slurry (i.e., solid fuel
suspended in water or another liquid) prior to gasification. Pumps convey
the slurry to the gasifier via a slurry injector. The concentration of
the solid fuel within the slurry is limited by the ability to pump the
slurry due to characteristics of the slurry, such as viscosity and
stability. Efforts to affect the solid fuel concentration within the
slurry, prior to pumping, include adding surfactants. However, even with
surfactants, the obtainable concentration is limited to concentrations
where the slurry is still stable and viscous enough for pumping.

[0018] Embodiments of the present disclosure provide a system that
includes at least one cross-flow filter configured to remove liquid
(e.g., water) from the slurry to concentrate the solid fuel prior to
gasification. For example, the system may include at least one cross-flow
filter disposed in the flow path of the slurry downstream of a fuel
slurry pump and upstream of a fuel slurry injector. The cross-flow filter
may include a filter medium that converges in a downstream direction
along the flow path of the slurry. Also, the cross-flow filter may
include multiple slurry flow paths. The system may include multiple
cross-flow filters disposed in parallel and/or series. Further, the
system may include an agitation system, a heating system, and/or a
purging system. Additional embodiments include a control system that
includes a controller configured to control the concentration of the
solid fuel in the slurry. For example, the controller may control the
slurry concentration by adjusting the amount of liquid (e.g., water)
removed from the slurry. Also, the controller may control the agitation
system, the heating system, and/or the purging system to improve water
removed in the filter. Further embodiments include a method for
controlling the concentration of the solid fuel in the fuel slurry with a
cross-flow filter prior to gasifying the slurry in a gasifier downstream
of the filter. For example, control may occur by adjusting the removal of
liquid from the slurry. In each of the disclosed embodiments, the systems
and methods are designed to concentrate the solid fuel in the slurry by
removing liquid from the slurry via a cross-flow filter.

[0019] Turning now to the figures, FIG. 1 is a schematic block diagram of
an embodiment of an integrated combined cycle (IGCC) system 100 utilizing
a filter 10 to increase solid fuel concentration in a slurry as mentioned
above. The filter 10 may be, e.g., a cross-flow filter 10. With the
cross-flow filter 10, the flow of the slurry travels tangentially across
a surface or filter medium of the filter 10. The cross-flow filter 10 may
be made of a high tensile material, such as a sintered metal alloy. The
metal alloy may include nickel, molybdenum, chromium, and/or tungsten, as
well as other metals and metal oxides. The filter medium of the filter 10
may include perforations of approximately 1 μm to 10 μm in
diameter, or any other suitable range. As the slurry flows tangentially
across the cross-flow filter 10 at a high velocity and a positive
pressure, liquid (e.g., water) is forced through the perforations as a
filtrate, while the solid fuel remains within the slurry. The flow of the
slurry prevents buildup of particles on the filter medium. Although the
cross-flow filter 10 is discussed with reference to the IGCC system 100
in FIG. 1, the disclosed embodiments of the cross-flow filter 10 may be
used in any suitable application (e.g., production of chemicals,
fertilizers, substitute natural gas, transportation fuels, or hydrogen).
In other words, the following discussion of the IGCC system 100 is not
intended to limit the disclosed embodiments to IGCC.

[0020] The IGCC system 100 produces and burns a synthetic gas, i.e.,
syngas, to generate electricity. Elements of the IGCC system 100 may
include a fuel source 102, such as a solid feed or solid fuel, that may
be utilized as a source of energy for the IGCC. The fuel source 102 may
include coal, petroleum coke, biomass, wood-based materials, agricultural
wastes, tars, asphalt, or other carbon containing items. The solid fuel
of the fuel source 102 may be passed to a slurry preparation unit 104.
The slurry preparation unit 104 may, for example, resize or reshape the
fuel source 102 by chopping, milling, shredding, pulverizing,
briquetting, or pelletizing the fuel source 102, then mix the fuel source
102 (e.g., coal) with a liquid solvent (e.g., water) to generate a fuel
slurry (e.g., coal slurry).

[0021] In the illustrated embodiment, a pump 12 delivers the feedstock
from the slurry preparation unit 104 to a filter 10 (e.g., cross-flow
filter 10). The filter 10 is configured to remove at least a portion of
the liquid from the fuel slurry to increase the concentration of the
solid fuel in the fuel slurry as described above. The filter 10 is
coupled to one or more valves 14. The valve 14 enables control of the
amount of liquid to be removed from the slurry. In certain embodiments,
the valve 14 may be used to allow the flow of liquid (e.g., water) into
the filter 10 to purge or clean the filter 10. The valve 14 is coupled to
a controller 16 (e.g., slurry concentration controller 16). The
controller 16 is configured to control removal of the liquid via the
filter 10 to adjust the concentration of the solid fuel in the fuel
slurry. For example, the controller 16 is configured to regulate the
valve 14, thus controlling the amount of liquid removed from the slurry.
In some embodiments, the controller 16 may be configured to control a
purge system via another valve 14 to clean or purge the filter 10. In
other embodiments, the controller 16 may also be configured to control
the concentration of the solid fuel in the fuel slurry by regulating an
agitation system and/or heating system.

[0022] From the filter 10, the slurry is delivered to a gasifier 106,
e.g., via a fuel slurry injector. The gasifier 106 converts the feedstock
102 into a syngas, e.g., a combination of carbon monoxide and hydrogen.
This conversion may be accomplished by subjecting the feedstock to a
controlled amount of steam and oxygen at elevated pressures, e.g., from
approximately 20 bar to 85 bar, and temperatures, e.g., approximately 700
degrees Celsius to 1600 degrees Celsius, depending on the type of
gasifier 106 utilized.

[0023] The gasification process includes the feedstock undergoing a
pyrolysis process, whereby the feedstock is heated. Temperatures inside
the gasifier 106 may vary during the pyrolysis process, depending on the
fuel source 102 utilized to generate the feedstock. The heating of the
feedstock during the pyrolysis process generates a solid, (e.g., char),
and residue gases, (e.g., carbon monoxide, hydrogen, and nitrogen). The
char remaining from the feedstock from the pyrolysis process may only
weigh up to approximately 30% of the weight of the original feedstock.

[0024] A partial oxidation process also occurs in the gasifier 106. The
oxidation process may include introducing oxygen to the char and residue
gases. The char and residue gases react with the oxygen to form carbon
dioxide and carbon monoxide, which provides heat for the gasification
reactions. The temperatures during the partial oxidation process may
range from approximately 700 degrees Celsius to 1600 degrees Celsius.
Steam may be introduced into the gasifier 106 during gasification. The
char may react with the carbon dioxide and steam to produce carbon
monoxide and hydrogen at temperatures ranging from approximately 800
degrees Celsius to 1100 degrees Celsius. In essence, the gasifier
utilizes steam and oxygen to allow some of the feedstock to be "burned"
to produce carbon monoxide and release energy, which drives a second
reaction that converts further feedstock to hydrogen and additional
carbon dioxide.

[0025] In this way, a resultant gas is manufactured by the gasifier 106.
This resultant gas may include approximately 85% of carbon monoxide and
hydrogen in equal proportions, as well as CH4, HCl, HF, COS,
NH3, HCN, and H2S (based on the sulfur content of the
feedstock). This resultant gas may be termed untreated, raw, or sour
syngas, since it contains, for example, H2S. The gasifier 106 may
also generate waste, such as slag 108, which may be a wet ash material.
This slag 108 may be removed from the gasifier 106 and disposed of, for
example, as road base or as another building material. Prior to cleaning
the raw syngas, a syngas cooler 107 may be utilized to cool the hot
syngas. The cooling of the syngas may generate high pressure steam which
may be utilized to produce electrical power as described below. After
cooling the raw syngas, a gas cleaning unit 110 may be utilized to clean
the raw syngas. The gas cleaning unit 110 may scrub the raw syngas to
remove the HCl, HF, COS, HCN, and H2S from the raw syngas, which may
include separation of sulfur 111 in a sulfur processor 112 by, for
example, an acid gas removal process in the sulfur processor 112.
Furthermore, the gas cleaning unit 110 may separate salts 113 from the
raw syngas via a water treatment unit 114 that may utilize water
purification techniques to generate usable salts 113 from the raw syngas.
Subsequently, the gas from the gas cleaning unit 110 may include treated,
sweetened, and/or purified syngas, (e.g., the sulfur 111 has been removed
from the syngas), with trace amounts of other chemicals, e.g., NH3
(ammonia) and CH4 (methane).

[0026] A gas processor 116 may be utilized to remove residual gas
components 117 from the treated syngas such as, ammonia and methane, as
well as methanol or any residual chemicals. However, removal of residual
gas components 117 from the treated syngas is optional, since the treated
syngas may be utilized as a fuel even when containing the residual gas
components 117, e.g., tail gas. At this point, the treated syngas may
include approximately 40% CO, approximately 40% H2, and
approximately 20% CO2 and is substantially stripped of H2S.
This treated syngas may be transmitted to a combustor 120, e.g., a
combustion chamber, of a gas turbine engine 118 as combustible fuel.
Alternatively, the CO2 may be removed from the treated syngas prior
to transmission to the gas turbine engine 118.

[0027] The IGCC system 100 may further include an air separation unit
(ASU) 122. The ASU 122 may operate to separate air into component gases
by, for example, distillation techniques. The ASU 122 may separate oxygen
from the air supplied to it from a supplemental air compressor 123, and
the ASU 122 may transfer the separated oxygen to the gasifier 106.
Additionally the ASU 122 may transmit separated nitrogen to a diluent
nitrogen (DGAN) compressor 124.

[0028] The DGAN compressor 124 may compress the nitrogen received from the
ASU 122 at least to pressure levels equal to those in the combustor 120,
so as not to interfere with the proper combustion of the syngas. Thus,
once the DGAN compressor 124 has adequately compressed the nitrogen to a
proper level, the DGAN compressor 124 may transmit the compressed
nitrogen to the combustor 120 of the gas turbine engine 118. The nitrogen
may be used as a diluent to facilitate control of emissions, for example.

[0029] As described previously, the compressed nitrogen may be transmitted
from the DGAN compressor 124 to the combustor 120 of the gas turbine
engine 118. The gas turbine engine 118 may include a turbine 130, a drive
shaft 131 and a compressor 132, as well as the combustor 120. The
combustor 120 may receive fuel, such as syngas, which may be injected
under pressure from fuel nozzles. This fuel may be mixed with compressed
air as well as compressed nitrogen from the DGAN compressor 124, and
combusted within combustor 120. This combustion may create hot
pressurized exhaust gases.

[0030] The combustor 120 may direct the exhaust gases towards an exhaust
outlet of the turbine 130. As the exhaust gases from the combustor 120
pass through the turbine 130, the exhaust gases force turbine blades in
the turbine 130 to rotate the drive shaft 131 along an axis of the gas
turbine engine 118. As illustrated, the drive shaft 131 is connected to
various components of the gas turbine engine 118, including the
compressor 132.

[0031] The drive shaft 131 may connect the turbine 130 to the compressor
132 to form a rotor. The compressor 132 may include blades coupled to the
drive shaft 131. Thus, rotation of turbine blades in the turbine 130 may
cause the drive shaft 131 connecting the turbine 130 to the compressor
132 to rotate blades within the compressor 132. This rotation of blades
in the compressor 132 causes the compressor 132 to compress air received
via an air intake in the compressor 132. The compressed air may then be
fed to the combustor 120 and mixed with fuel and compressed nitrogen to
allow for higher efficiency combustion. Drive shaft 131 may also be
connected to load 134, which may be a stationary load, such as an
electrical generator for producing electrical power, for example, in a
power plant. Indeed, load 134 may be any suitable device that is powered
by the rotational output of the gas turbine engine 118.

[0032] The IGCC system 100 also may include a steam turbine engine 136 and
a heat recovery steam generation (HRSG) system 138. The steam turbine
engine 136 may drive a second load 140. The second load 140 may also be
an electrical generator for generating electrical power. However, both
the first and second loads 134, 140 may be other types of loads capable
of being driven by the gas turbine engine 118 and steam turbine engine
136. In addition, although the gas turbine engine 118 and steam turbine
engine 136 may drive separate loads 134 and 140, as shown in the
illustrated embodiment, the gas turbine engine 118 and steam turbine
engine 136 may also be utilized in tandem to drive a single load via a
single shaft. The specific configuration of the steam turbine engine 136,
as well as the gas turbine engine 118, may be implementation-specific and
may include any combination of sections.

[0033] The IGCC system 100 may also include the HRSG 138. High pressure
steam may be transported into the HSRG 138 from the syngas cooler 107.
Also, heated exhaust gas from the gas turbine engine 118 may be
transported into the HRSG 138 and used to heat water and produce steam
used to power the steam turbine engine 136. Exhaust from, for example, a
low-pressure section of the steam turbine engine 136 may be directed into
a condenser 142. The condenser 142 may utilize a cooling tower 128 to
exchange heated water for chilled water. The cooling tower 128 acts to
provide cool water to the condenser 142 to aid in condensing the steam
transmitted to the condenser 142 from the steam turbine engine 136.
Condensate from the condenser 142 may, in turn, be directed into the HRSG
138. Again, exhaust from the gas turbine engine 118 may also be directed
into the HRSG 138 to heat the water from the condenser 142 and produce
steam.

[0034] In combined cycle systems such as IGCC system 100, hot exhaust may
flow from the gas turbine engine 118 and pass to the HRSG 138, along with
the steam generated by the syngas cooler 107, where it may be used to
generate high-pressure, high-temperature steam. The steam produced by the
HRSG 138 may then be passed through the steam turbine engine 136 for
power generation. In addition, the produced steam may also be supplied to
any other processes where steam may be used, such as to the gasifier 106.
The gas turbine engine 118 generation cycle is often referred to as the
"topping cycle," whereas the steam turbine engine 136 generation cycle is
often referred to as the "bottoming cycle." By combining these two cycles
as illustrated in FIG. 1, the IGCC system 100 may lead to greater
efficiencies in both cycles. In particular, exhaust heat from the topping
cycle may be captured and used to generate steam for use in the bottoming
cycle.

[0035] FIGS. 2-7 illustrate various embodiments of filtration systems
associated with the filter 10. FIG. 2 is a schematic block diagram of an
embodiment of a filtration system 152 employed upstream of a gasifier
106. The filtration system 152 is designed to increase the concentration
of solid fuel within a fuel slurry prior to gasification, but subsequent
to pumping of the fuel slurry. The filtration system 152 includes the
filter 10 disposed in a slurry flow path, indicated generally by arrow
154, downstream of a fuel slurry pump 12. The filter 10 is also disposed
upstream of a fuel slurry injector 156. The filter 10 may be a cross-flow
filter 12 as described above. Upstream of the slurry pump 12, a slurry
mixing tank 158 is configured to prepare the fuel slurry by mixing solid
fuel with liquid (e.g., water) to create a suspension. The slurry mixing
tank 158 is configured to deliver the fuel slurry to the slurry pump 12.
The slurry pump 12 is configured to pump the fuel slurry along the slurry
flow path 154 having the cross-flow filter 10. The slurry flow path 154
extends through an enclosure 160 of the cross-flow filter 10. In
addition, the slurry flow path 154 is surrounded by a filter medium 162.
For example, the filter medium 162 may be a hollow cylindrical (e.g.,
annular) filter medium, which may be offset from an outer wall 161 of the
enclosure 160 by an offset distance 163. The filter medium 162 may be
welded to the enclosure 160. The filter medium 162 includes perforations
164 as described above. The cross-flow filter 10 is configured to remove
at least a portion of the liquid from the fuel slurry to increase the
concentration of the solid fuel in the fuel slurry. As the fuel slurry
flows tangentially along the slurry flow path 154 and through the
cross-flow filter 10, a portion of the liquid is forced through the
perforations 164 of the filter medium 162, as indicated generally be
arrows 166, as a filtrate due to high velocity and positive pressure. The
high velocity and positive pressure also maintains the solid fuel within
the fuel slurry as well as the solid fuel moving along the slurry flow
path 154, thus, the concentration of the solid fuel within the fuel
slurry is increased. The flow of the fuel slurry also cleans the filter
medium 162 resulting in self-cleaning of the filter 10. The filter 10 may
remove any amount of the liquid from the fuel slurry. For example, the
filter 10 may remove 1 to 20, 1 to 10, or 1 to 5 percent of the liquid
from the fuel slurry.

[0036] The pressure within the filter 10 may range from 400 psi to 1400
psi. For example, the pressure may be 400, 500, 600, 700, 800, 900, 1000,
1100, 1200, 1300, and 1400, or any pressure therebetween. Beside
pressure, other factors of the filter 10 may be adjusted that affect the
flow of the fuel slurry. A length 167 (e.g., for a pipeline) between the
pump 12 and the gasifier 106 may range from approximately 100 feet to 300
feet. For example, the length 167 may be approximately 100, 125, 150,
175, 200, 225, 250, 275, or 300 feet, or any distance therebetween. A
length 168 of the filter 10 may range from approximately 6 feet to 50
feet or any other suitable length. For example, the filter length 168 may
be approximately 6, 10, 20, 30, 40, or 50 feet, or any distance
therebetween. A width 170 of the filter medium 162 within the filter 10
may range from approximately 4 inches to 8 inches or any other suitable
width. For example, the width 170 may be approximately 4, 5, 6, 7, or 8
inches, or any distance therebetween. Adjustment of the length 168 of the
filter 10 and the width 170 of the filter medium 162 may allow control of
both the flow velocity as well as the pressure within the filter 10.

[0037] Upon flowing through the filter 10, the slurry fuel is received by
the slurry injector 156. The slurry injector 156 is configured to receive
and inject the fuel slurry into the gasifier 106. The gasifier 106 is
configured to generate a syngas, as described above, from the fuel
slurry. Increasing the concentration of the solid fuel in the fuel slurry
post-pumping may improve carbon conversion and cold gas efficiency in the
gasification of the fuel slurry, while avoiding the problems associated
with pumping higher concentrated slurries.

[0038] The filtration system 152 also includes a control system 172
configured to control removal of the liquid (e.g., water) via the
cross-flow filter 10 to adjust the concentration of the solid fuel in the
fuel slurry. The control system 172 includes controller 16 (e.g., slurry
concentration controller 16). The controller 16 is configured to control
the concentration of the solid fuel in the fuel slurry for gasification.
In particular, the controller 16 is configured to adjust removal of the
liquid from the fuel slurry via the cross-flow filter 10. In certain
embodiments, a valve 174 maintains the flow rate of the liquid removed
from the fuel slurry at a constant rate to control the concentration. In
other embodiments, the valve 174 may be controlled to provide a variable
flow rate based on the feedback. The liquid removed or filtrate is
recirculated to the slurry mixing tank 158, as generally indicated by
arrow 176, for mixing with solid fuel to form more fuel slurry. The
controller 16 is coupled to the valve 174. The controller 16 determines
the flow rate of the liquid removed by adjusting valve 174. For example,
the valve 174 may be closed to prevent the removal of liquid from the
fuel slurry. Alternatively, the valve 174 may be opened to a varying
degree to determine the flow rate of liquid removed. The controller 16 is
responsive to user input and feedback to adjust the flow rate. For
example, controller 16 may be responsive to feedback from system
components related to the concentration of the solid fuel in the fuel
slurry. By further example, the feedback may come from transducers
located at various system components, such as the slurry mixing tank 158,
the slurry pump, the valve 174, and/or the slurry injector 156. The
feedback may also be indirectly related to the concentration of the solid
fuel in the fuel slurry. For example, transducers may be located at the
gasifier 106 to provide feedback as to the performance of the gasifier
106 or the heating value of the fuel slurry, which may be indirect
indicators of the concentration of the solid fuel in the fuel slurry. The
feedback may include an actual measurement of the concentration of the
solid fuel in the fuel slurry. Also, the feedback may include
measurements of other parameters indirectly related to the concentration
of the solid fuel in the fuel slurry, such as temperature, pressure,
and/or other parameters. From the feedback, the concentration of the
solid fuel in the fuel slurry is controlled via the cross-flow filter 10.

[0039] Embodiments of the filtration system 152 may include multiple
filters 10. FIG. 3 is schematic block diagram of an embodiment of the
filtration system 152 employing multiple filters 10 in parallel. As
above, the filtration system 152 is designed to increase the
concentration of solid fuel within the fuel slurry prior to gasification,
but subsequent to pumping of the fuel slurry. The filtration system 152
includes both a first cross-flow filter 186 and a second cross-flow
filter 188 disposed in parallel along first and second slurry flow paths,
respectively, indicated generally by arrows 190 and 192, downstream of
the fuel slurry pump 12. In other embodiments, the filtration system 152
may include more than 2 filters 10 in parallel. For example, the
filtration system 152 may include 3 to 5 or more filters 10. The slurry
pump 12 is coupled to the slurry mixing tank 158 disposed upstream of the
pump 12. The slurry mixing tank 158 and the slurry pump 12 are as
described above. The cross-flow filters 186 and 188 are also disposed
upstream of the fuel slurry injector 156. The fuel slurry injector 156 is
coupled to the gasifier 106 disposed downstream of the fuel slurry
injector 156. The fuel slurry injector 156 and the gasifier 106 are as
described above.

[0040] Each cross-flow filter 186 and 188 operates individually as
described above. The first cross-flow filter 186 is configured to remove
at least a first portion of the liquid from the fuel slurry, while the
second cross-flow filter is configured to remove at least a second
portion of the liquid from the fuel slurry. The cross-flow filters 186
and 188 may be operated separately or simultaneously by the control
system 172. In particular, the controller 16 controls each cross-filter
186 and 188 as described above. For example, the controller 16 is coupled
to valves 194 and 196 of filters 186 and 188, respectively, and
configured to control the concentration of the solid fuel in the fuel
slurry. Removed liquid from the fuel slurry is recirculated to the slurry
mixing tank 158, as indicated generally by arrows 198 and 200. The
controller 16 is also coupled to valves 201 and 202 disposed in the first
and second slurry flow paths 190 and 192, respectively, between the
slurry pump 12 and the filters 186 and 188. By opening and closing valves
201 and 202, the controller 16 determines if one or both of the
cross-flow filters 186 and 188 may be used in the filtration system 152.
For example, the controller 16 may open valve 201 allowing the use of the
first cross-flow filter 186, while closing valve 202 preventing the used
of the second cross-flow filter 188, and vice versa. Alternatively, the
controller 16 may open both valves 200 and 202 allowing the use of both
filters 186 and 188. When using both filters 186 and 188, the controller
16 may adjust the valves 201 and 202 to allow the same and/or different
flow amounts of fuel slurry. In addition, when both filters are used
simultaneously, the controller 16 can adjust valves 194 and 196 to allow
the same and/or different removal rates of liquid from the fuel slurries
in the respective slurry flow paths 190 and 192.

[0041] In addition, the controller 16 controls purging or cleaning of the
filters 186 and 188. The controller 16 is coupled to valves 204 and 206
disposed in the first and second slurry flow paths 190 and 192,
respectively, downstream of the filters 186 and 188 and upstream of the
fuel slurry injector 156. Opening of valves 204 and 206 allows the
concentrated fuel slurry to flow to the fuel slurry injector 156, and
then the gasifier 106 as described above. In addition, the controller 16
is coupled to valves 208 and 210. The controller 16 controls the opening
and closing of valves 208 and 210 to allow a flow of liquid (e.g., water)
from a liquid source 212 (e.g., flush water) to flush the filters 186 and
188. For example, the controller 16 may close valves 194, 196, 201, 202,
204, and 206, and open valves 194, 196, 208, and 210 to allow the
cleaning of the each filter medium 162 of the filters 186 and 188 by the
flushing liquid. The flushing liquid flows upstream through filters 186
and 188 and subsequently paths 198 and 200 to the slurry mixing tank 158
for mixing of the liquid with the solid fuel to form more fuel slurry.
Conversely, valves 208 and 210 may be closed, and the other valves opened
to enable control of the concentration of the solid fuel in the fuel
slurry. However, by opening the valves 194, 196, 208, and 210, the
controller 16 is configured to allow purging in both filters 186 and 188
simultaneously or individually. In addition, the controller 16 is
configured to enable control of the concentration of the solid fuel in
one filter 186 or 188, while simultaneously allowing purging in the other
filter 186 or 188. Use of multiple filters 10 in parallel may allow the
removal of more moisture from the fuel slurry than an individual filter
10. In addition, having multiple filters 10 in parallel allows the
operation of one filter 10, when the other filter 10 is not available for
use (e.g., in need of servicing).

[0042] Besides filters 10 in parallel, the filtration system 152 may
include filters 10 in series. FIG. 4 is a schematic block diagram of an
embodiment of the filtration system 152 employing multiple filters 10 in
series. As above, the filtration system 152 is designed to increase the
concentration of the solid fuel within the fuel slurry prior to
gasification, but subsequent to pumping of the solid fuel slurry. The
filtration system 152 includes both the first cross-flow filter 186 and
the second cross-flow filter 188 disposed in series along the slurry flow
path 154 downstream of the fuel slurry pump 12, where filters 186 and 188
are configured to remove at least first and second portions,
respectively, of the liquid from the fuel slurry. In other embodiments,
the filtration system 152 may include more than 2 filters 10 in series.
For example, the filtration system may include 3 to 5 or more filters 10.
As described above, the slurring mixing tank 158 is disposed upstream of
the filters 186 and 188, while the slurry fuel injector 156 and the
gasifier 106 are disposed downstream of the filters 186 and 188.

[0043] As above, the cross-flow filters 186 may be operated separately or
simultaneously via the control system 172. The controller 16 controls
each cross-filter 186 and 188 as described above. For example, the
controller 16 is coupled to valves 222 and 224 of filters 186 and 188,
respectively, and configured to control the concentration of the solid
fuel in the fuel slurry via removal of the liquid from the fuel slurry.
As above, the controller 16 can adjust valves 222 and 224 to allow the
same and/or different removal rates of liquid from the fuel slurry in the
same slurry flow path 154. The removed liquid is recirculated back to the
mixing tank via paths 226 and 228 to produce more fuel slurry as
described above. Also, as described above, the controller 16 is coupled
to valves 230 and 232 to allow the flushing of filters 186 and 188 with
liquid (e.g., water) from flushing liquid source 212.

[0044] The controller 16 is coupled to valves 234 and 236 to control flow
of the fuel slurry into and out of the first cross-flow filter 186. The
controller 16 is also coupled to valves 238 and 240 to control the flow
of the fuel slurry into and out of the second cross-flow filter 188. In
addition, the controller 16 is coupled to valves 240 and 242 to allow
bypass of the first cross-flow filter 186 when valves 240 and 242 are
open and valves 234 and 236 are closed. The controller 16 is coupled to
valves 244 and 246 to allow bypass of the second cross-flow filter 188
when valves 244 and 246 are open and valves 238 and 240 are closed. The
coupling of the controller 16 to all of these valves allows the
controller 16 to control the removal of water from the fuel slurry using
filters 186 and 188 either serially or individually. Using the filters
186 and 188 serially may allow the solid fuel to be concentrated in the
fuel slurry to a greater extent than using either filter 186 or 188
individually. In addition, the controller 16 is configured to control
simultaneous or independent purging of the filters 186 and 188. Further,
the controller 16 is configured to enable control of the concentrating of
the solid fuel in the fuel slurry using filter 186 or 188, while
simultaneously purging the other filter 186 or 188. The controller 16, as
above, is responsive to user input as to the flow rate as well as
responsive to feedback from system components related to the
concentration of the solid fuel in the fuel slurry. For example, the
feedback may come from transducers located at various system components,
e.g., the mixing tank 158, slurry injector 156, and/or gasifier 106. As
described above, the feedback may be direct or indirect measurements
related to solid fuel concentration in the fuel slurry.

[0045] Besides including multiple filters 10, the filtration system 152
may include filters 10 with different embodiments to help concentrate the
solid fuel in the fuel slurry. FIG. 5 is a schematic block diagram of an
embodiment of the filtration system 152 employing multiple flow passages
within the filter 10. As above, the slurry mixing tank 158 and slurry
pump 12 are disposed upstream of the cross-flow filter 10. The slurry
injector 156 is disposed downstream of the filter 10. Also, as above, the
controller 16 controls the removal of liquid from and the purging of the
filter 10 via valves 256 and 258, respectively. The illustrated
cross-flow filter 10 includes enclosure 160 and multiple slurry flow
paths 260, 262, and 264 extending through the enclosure 160. Each slurry
flow path 260, 262, and 264 is surrounded by filter medium 162 (e.g., an
annular filter medium). The fuel slurry is received by the filter 10 near
an inlet 265 of the filter 10, whereupon the fuel slurry is divided among
slurry flow paths 260, 262, and 264. Liquid (e.g., water) is then removed
from the fuel slurry as the slurry flows tangentially across each filter
medium 162 of each slurry flow path 260, 262, and 264 as described above.
The removed liquid or filtrate is recirculated back to the slurry mixing
tank via path 267 to be used in preparing more fuel slurry. After flowing
through each filter medium 162, the concentrated slurry exits the filter
10 at outlet 266 to the slurry injector 156 for injection to the gasifier
106. The use of multiple flow passages may increase the amount of liquid
that may be removed from the slurry, thus, concentrating the solid fuel
within the fuel slurry prior to gasification. As a result, carbon
conversion and cold gas efficiency may be improved in the gasification of
the fuel slurry.

[0046] Alternatively, the filtration system 152 may include filter 10 that
converges. For example, FIG. 6 is a schematic block diagram of an
embodiment of the filtration system 152 employing a converging filter 10.
The filtration system 152 and other components are as described in FIG. 5
except for the filter design. The illustrated cross-flow filter 10
includes enclosure 160. The cross-flow filter 10 includes a slurry flow
path, indicated generally by arrow 274, extending through the enclosure
160. The slurry flow path 274 is surrounded by filter medium 162. The
filter medium 162 converges in a downstream direction along the slurry
flow path 274 from the inlet 265 to the outlet 266 of the cross-flow
filter 10. For example, the filter medium 162 may be a hollow conical
filter medium 162. As the fuel slurry enters at the inlet 265, the filter
medium 162 has width 276. As the concentrated fuel slurry exits at outlet
266, the filter medium 162 has width 278. In certain embodiments, the
width 276 may range from approximately 2 to 10 times larger than width
278. For example, the width 276 may be approximately 2, 4, 6, 8, or 10
times larger than width 278. The converging filter medium 152 creates
more shear along its surface as the slurry flows downstream. The
increased shear may result in the removal of more liquid from the fuel
slurry by the filter medium 162, as generally indicated by arrows 280.
The removal of more liquid may allow a higher concentration of the solid
fuel in the fuel slurry prior to gasification. As described above, the
removed liquid or filtrate is recirculated via path 267 to the slurry
mixing tank 158. In the illustrated embodiment, an inlet 282 to liquid
removal path 267 is located more towards the outlet 264 of the filter 10,
since a larger portion of removed liquid may be located towards that
portion of the filter 10. In other embodiments, the inlet 282 to path 267
may be disposed along other portions of the filter 10.

[0047] As previously mentioned, the filtration system 152 may include
other systems for helping concentrate the solid fuel in the fuel slurry.
FIG. 7 is a schematic block diagram of an embodiment of the filtration
system 152 employing agitation and heating systems. As above, the
filtration system 152 includes the filter 10 disposed in the slurry flow
path 154 downstream from the fuel slurry pump 12 as well as upstream of
the fuel slurry injector 156. As above, the cross-flow filter 10 includes
enclosure 160 and filter medium 162. The filter 10 may remove liquid from
the fuel slurry as described above. Besides the filter 10, the filtration
system 152 includes an agitation system 290 and a heating system 292
coupled to the cross-flow filter 10. The agitation system 290 includes an
agitator 294 coupled to a drive 296. The drive 296 is configured to cause
the agitator 294 to agitate. The agitator 294 is configured to agitate
the cross-flow filter 10. As illustrated, the agitator 294 is disposed on
an outer surface 298 of the enclosure 160. In certain embodiments, the
agitator 294 is disposed within an inner volume 300 of the filter 10. For
example, the agitator 294 may be located on an inner surface 302 of the
enclosure 160 or directly on the filter medium 162. Agitation or
vibration of the cross-flow filter 10 removes any potential filter cake
or particles that may bind to the filter medium 162. This keeps the
filter 10 clean and allows a constant removal of the liquid from the fuel
slurry to concentrate the solid fuel in the slurry.

[0048] As mentioned, the filtration system 152 includes the heating system
292. The heating system 292 includes at least one heater 304 configured
to heat the cross-flow filter 10. Heating of the cross-flow filter 10
allows the removal of more liquid from the fuel slurry to further
concentrate the solid fuel in the fuel slurry. The heater 304 may include
a heating element 306 and a heat exchanger 308. As illustrated, the
heating element 306 and the heat exchanger 308 are disposed within the
inner volume 300 of the filter 10 on the inner surface 302 of the
enclosure 160. In other embodiments, the heating element 306 and/or heat
exchanger 308 may be disposed directly on the filter medium 162.
Alternatively, the heating element 306 and/or heat exchanger 308 may be
disposed on the outer surface 298 of the enclosure 160.

[0049] Heat is provided to the heating element 306 via an external heat
source 310. The heat source 310 may include steam, combustion exhaust
(e.g., from a gas turbine, boiler, or furnace), heated process water, or
waste heat. For example, the waste heat may be obtained from a variety of
plant components, such as a gas treatment unit, a compressor, an engine,
or a component of an integrated gasification combined cycle (IGCC)
system. A heat exchanger 312 may transfer heat from a variety of plant
components 314 or external heat source to heat exchanger 308, and then
heat exchanger 308 may transfer the heat directly to the cross-flow
filter 10 or indirectly with a heat transfer medium. For example, the
heat exchanger 308 may transfer heat to the enclosure 160, the inner
volume 300 of the filter 10, or the filter medium 162.

[0050] The controller 16 (e.g., slurry concentration controller 16) is
coupled to both the agitation system 290 and the heating system 292. The
controller 16 is configured to control the agitation system 290 to
agitate the cross-flow filter 10. The controller 16 may be responsive to
feedback, as described above, to control the agitation system 290. Also,
the controller 16 is configured to control the heating system 292 to heat
the cross-flow filter 10. For example, the controller 16 is coupled to
the heat source 310 to control the heat provided to the heating element
306. In addition, the controller 16 is coupled to valves 316 and 318 to
control the exchange of heat from the plant components 314 to heat
exchanger 312 as well as the transfer of heat from heat exchanger 312 to
heat exchanger 308, and then to the cross-flow filter 10. The controller
16 may be responsive to feedback, as described above, to control the
heating system 292. Control of the agitation system 290 and the heating
system 292, as well as liquid removal as described above, allow the
controller 16 to determine the amount of liquid removed from the fuel
slurry to concentrate the solid fuel in the fuel slurry.

[0051] In certain embodiments, a method may include concentrating the fuel
slurry via cross-flow filtration and gasifying the concentrated fuel
slurry. For example, the method may include controlling the concentration
of the solid fuel in the fuel slurry at least partially by adjusting
removal of the liquid from the fuel slurry via the cross-flow filter 10
as described above. Controlling the concentration may include controlling
agitation of the cross-flow filter 10 as described above. Also,
controlling the concentration may include controlling heating of the
cross-flow filter 10 as described above. Further, the method may include
gasifying the fuel slurry in the gasifier 106 downstream from the
cross-flow filter 10.

[0052] Technical effects of the disclosed embodiments include employing
cross-flow filtration of the fuel slurry downstream of the fuel slurry
pump 12 and upstream of the fuel slurry injector 156. Disposing the
cross-flow filter 10 between the pump 12 and injector 156 allows liquid
to be removed from the fuel slurry to obtain a higher concentration of
solid fuel in the slurry post-pumping. Increasing the obtainable
concentration levels of the solid fuel in the fuel slurry post-pumping
avoids problems associated with pumping higher concentration slurries and
may also improve carbon conversion and cold gas efficiency in the
gasification of the fuel slurry. The desired concentration may also be
regulated via the control system 172.

[0053] This written description uses examples to disclose the invention,
including the best mode, and also to enable any person skilled in the art
to practice the invention, including making and using any devices or
systems and performing any incorporated methods. The patentable scope of
the invention is defined by the claims, and may include other examples
that occur to those skilled in the art. Such other examples are intended
to be within the scope of the claims if they have structural elements
that do not differ from the literal language of the claims, or if they
include equivalent structural elements with insubstantial differences
from the literal language of the claims.